1. Field of the Invention
The invention relates to a method for measuring a bonding force and, particularly, to a method for measuring a bonding force between a substrate and a carbon nanotube array formed thereon.
2. Description of Related Art
Carbon nanotubes (CNTs) are a carbonaceous material discovered by Iijima, a researcher of NEC Corporation, in 1991. Carbon nanotubes are electrically conductive along their length, are chemically stable, and can each have a very small diameter (much less than 100 nanometers) and a large aspect ratio (i.e., the ratio of length to diameter). Due to these and other properties, it has been suggested that carbon nanotubes can play an important role in fields such as microscopic electronics, field emission devices, thermal interface materials, etc.
Generally, a CNT field emission display device includes a substrate and a carbon nanotube array formed on the substrate. The carbon nanotube array acts as an electron emitter for emitting electrons, which collide with a phosphor layer disposed opposite to the carbon nanotube array, thereby stimulating light emission upon such collision. A bonding force or strength between the carbon nanotube array and the substrate is considered an important factor related to the performance of the CNT field emission display. Undesirable phenomena, such as short circuits, electrical discharges, or complete electrical disconnects, may occur if the bonding force between the carbon nanotube array and the substrate is weak. Therefore, it is important to determine whether the bonding force between the carbon nanotube array and the substrate is strong enough to guarantee good performance of the CNT field emission display, especially over a suitable lifetime for such. Thus, a method for effectively measuring the bonding force between the substrate and the carbon nanotube array is needed.
The conventional methods employed to measure the bonding force usually use an atomic force microscope (AFM) or an mN force gauge. The AFMs suffer from the limitation that they can merely measure a single carbon nanotube or a few carbon nanotubes at a time. Therefore, it can be seen that it is impractical to use AFMs to measure the carbon nanotubes in mass production. In addition, a Van der Waals force between each carbon nanotubes will interfere with the measuring results, so that the precision of measuring results is decreased accordingly. For example, added Van der Waals force between proximate carbon nanotubes can create the appearance of a larger carbon nanotube to substrate bonding force than what actually exists.
However, the mN force gauge will generate noise during measurement, due much in part to the aforementioned Van der Waals force that exists between adjoining carbon nanotubes. A signal-to-noise ratio of measurement is relative low, thus making it difficult to make accurate and/or precise measurements.
What is needed, therefore, is a method for measuring a bonding force between a substrate and a carbon nanotube array formed thereon that has improved efficiency and provides more precise measuring results of such bonding force.